To study spatial organization and determination in Drosophila embryos, we will characterize embryonic lethal mutations with major zygolic effects on early spatial pattern. A major part of the analysis will concentrate on the two x-linked loci necessary for normal morphogenetic movements at gastrulation. Folded and twisted gastrulation are among the earliest acting genes in Drosophila required within 3 1/2 h after fertilization. We will make amorphic and hypomorphic alleles, determine precise cytogenetic localization, look for intra- and intergenic suppressor mutations and carry out hybrid dysgenesis to obtain alleles useful in the molecular cloning. Morphological studies of sectioned material (light microscopic and EM) will be used to define the cellular defects associated with abnormal morphogenesis. Mosaics produced by ring-x loss and nuclear transportation will be used to define the precise regional requirements for gene activity. We will continue our work on segmentation mutants carrying out detailed analysis of even stripped, odd stripped, armadillo to complement studies of runt and Kruppel. Genetic mosaics will be used to determine cellular autonomy of loci and double mutants will be constructed to detect interactions. We will complete the characterization of the maternal effect mutations in particular those which have effects on early embryonic development. In addition the appropriate maternal loci will be tested for specific interactions with zygolic lethal mutations.